1. Field of the Invention
The present invention relates generally to a disc drive device and, more particularly, to a disc drive device for rotationally driving a disc-shaped recording medium such as a magnetic disc or an opto-magnetic disc.
2. Description of the Related Art
Magnetic discs are known as recording media for recording various kinds of information such as data, images or sound. For example, electronic still cameras utilize magnetic discs for image recording. In such an electronic still camera, a video signal outputted from an image sensor is recorded on a magnetic disc called a still video floppy disc. One field of video signal can be recorded on each track, and it is prescribed that, in the case of frame-image recording, odd and even fields of video signals are recorded on adjacent two tracks. A standard still video floppy disc is provided with fifty tracks and can record fifty field images or twenty-five frame images.
A typical mechanism for driving a still video floppy disc includes a spindle motor for causing the still video floppy disc to rotate and a head movement mechanism for causing a magnetic head to move radially with the floppy disc. The head movement mechanism includes a carriage for carrying the magnetic head, a stepping motor for generating a driving force for head movement, and a rotary motion-to-linear motion converting mechanism, such as a leadscrew or a cam, for converting the rotary motion of the stepping motor to the linear motion of the carriage. The movement distance of the magnetic head is determined by the number of pulses applied to the stepping motor, and it is prescribed that the magnetic head moves by one track (0.1 mm radially) by the application of, for example, four pulses. In other words, open-loop control is adopted which does not use electrical feedback.
Regarding control of head touch, in addition to a positive-pressure pad system for applying a positive pressure by using a pad, a negative-pressure pad system is known in which a negative-pressure type of pad is provided around a magnetic head and a negative pressure is generated between a floppy disc and the pad by the motion of air flow near the floppy disc which is rotating so that the contact between the magnetic head and the floppy disc is stabilized.
Recording timing for such a still video floppy disc is explained in brief. Signals are concentrically recorded with a 60-.mu.m track width and on 100-.mu.m track pitch, and recording on each track is started by making reference to a starting point, i.e., the center of a PG yoke provided on the still video floppy disc. A PG signal obtained by detecting the PG yoke is generated once for one rotation of the floppy disc, and the leading edge of a vertical synchronizing signal Vs appears when a 7H period (1H is one horizontal synchronizing period) passes after the detection of the PG signal. A vertical blanking period including the vertical synchronizing signal Vs is a period of approximately 20H which starts 3H before the vertical synchronizing signal Vs, and video signals for one field are recorded after the vertical blanking period.
However, the conventional negative-pressure pad has the problem that if a disc-shaped recording medium manufactured by a particular magnetic-disc maker curves in a direction away from the negative-pressure head or if a disc-shaped recording medium curves in such a direction owing to its deformation under high- or low-temperature conditions, no negative pressure is generated while the disc-shaped recording medium is rotating and no predetermined head touch is obtained between the disc-shaped recording medium and the magnetic head, with the result that no recording can be performed.
To cope with the above-described problem, an arrangement has been proposed in which an upper pad for suppressing the curvature of the disc-shaped recording medium is provided on the side of the disc-shaped recording medium that is opposite to the negative-pressure pad. However, this arrangement still has the following problems. The first problem is that the distance between the upper pad and the disc-shaped recording medium must be set with high precision and the second problem is that since the upper pad presses against the disc-shaped recording medium, the magnetic head and the disc-shaped recording medium easily wear severely to lower the durability of the disc drive device itself.
A disc drive device employing this kind of negative-pressure pad has the problem that if a disc-shaped recording medium and the negative-pressure pad are spaced apart from each other in excess of a distance within which the disc-shaped recording medium can be drawn to the negative-pressure pad by suction, the negative-pressure pad cannot draw the disc-shaped recording medium by suction even after the disc-shaped recording medium has started rotating. To solve this problem, such a disc drive device is provided with a restraining member for forcibly pressing the disc-shaped recording medium upon mounting thereof until the disc-shaped recording medium reaches the distance within which it can be drawn by suction to the negative-pressure pad. When the disc-shaped recording medium is drawn to the negative-pressure pad by suction, it is separated from the restraining member by the suction operation of the negative-pressure pad.
FIGS. 1(A) and 1(B) show one example of the disc drive device provided with the above-described restraining member.
FIG. 1(A) shows the state of a magnetic disc being unmounted and FIG. 1(B) shows the state of the magnetic disc being mounted. The shown example includes a chassis 101 of a recording or reproducing apparatus, a magnetic medium 102 on which information is to be recorded, a hard case 103 in which the magnetic medium 102 is accommodated, a spindle motor 104 for rotationally driving the magnetic medium 102 at a predetermined rotational speed, a restraining member 105 supported turnably at one end by a mounting portion 107 of the chassis 101 to restrain the rotational fluctuations of the magnetic medium 102, and an engagement portion 106 provided in the restraining member 105 for holding the restraining member 105 in the state shown in FIG. 1(A) by being maintained in contact with the hard case 103 when the magnetic disc is in an unmounted state.
The shown example also includes a head 108 for recording or reproducing information on or from the magnetic medium 102, and a pad 109. The pad 109 is fixed to the head 108 and has one surface provided with a groove. When the magnetic medium 102 is made to rotate, a negative pressure is generated by the groove to draw the magnetic medium 102 by suction.
In the recording or reproducing apparatus provided with the above-described arrangement, if the magnetic disc is in the unmounted state shown in FIG. 1(A), the restraining member 105 is kept away from the magnetic medium 102. If the magnetic disc is shifted to the mounted state of FIG. 1(B), the restraining member 105 is made to move to its restraining position in interlocked relation to this shift, whereby the rotational fluctuations or curvature of the magnetic medium 102 occurring during the rotation thereof is reduced by the restraining member 105 to cause the pad 109 to securely generate a negative pressure, thereby drawing the magnetic medium 102 to the pad 109 by suction. Thus, the magnetic medium 102 is maintained in stable head touch relative to the head 108.
However, such a recording or reproducing apparatus has a number of problems. For example, the restraining member is at all times located in the restraining position when the magnetic disc is in the mounted state, that is, the restraining member remains in the restraining position even after the pad has drawn the magnetic medium by suction. As a result, if the rotational fluctuations or the like of the magnetic medium occur during the rotation thereof, the magnet medium may come into contact with the restraining member.
FIG. 2 is a graph showing the positional relation between the magnetic medium and the restraining member. In FIG. 2, a waveform (a) indicates the waveform obtained when the magnetic medium is not being rotationally driven, and a waveform (b) indicates the waveform obtained when the magnetic medium is being rotationally driven.
As can be seen from the waveform (b), during the rotational drive of the magnetic medium, a phenomenon actually occurs in which the position of the restraining member partially coincides with the waveform of the rotational fluctuations of the magnetic medium and the restraining member and the magnetic medium are in partial contact with each other.
This phenomenon not only causes the rotational fluctuations of a rotating system but also leads to the problem that the magnetic medium is damaged during the long-time rotational drive thereof.